Patent GB-409110-A (GB)
Title: Improvements in or relating to a method of and apparatus for separating wax from oil
IPC: C10G73/06
Filed: 1933-02-23
Abstract: In the process for dewaxing oils described in the parent Specification the wax-containing oil is dissolved in a liquefied normally gaseous substance and the solution is chilled at a rate of \ba1/2\be to 8 DEG  F. per minute.  Shock chilling is avoided by bringing the cooling chambers to the same temperature as the solution before introduction therein.  Suitable diluents consists of propane, butane, isobutane, ethane, ethylene, propylene, butylene, alkyl ethers such as methyl or dimethyl ether, alkylene ethers, halogenated hydrocarbons such as methyl chloride, dichlor-difluor-methane, or oxygenated compounds such as ethylene oxide which are normally gaseous.  Pentane and hexane may also be used preferably under reduced pressure.  Wax bearing oil passes from one of the gauging tanks 30, Fig. 1, to a mixer 32 in which it is commingled with an equal volume of cooled-liquefied propane admitted from one of a series of tanks 12.  The mixture passes through a heat exchanger 35 in which mixture is brought to a temperature of about 90 DEG  F. to <PICT:0409110/III/1> <PICT:0409110/III/2> form a solution which is then admitted to one of a series of chillers A--D which have been warmed to 90 DEG  F. by steam coils or by condensation of propane vapours.  The solution is then chilled to - 40 DEG  F. at the rate of 3 DEG  F. per minute by addition of used "wash" propane obtained from filters L, M, N and by evaporation of propane through pipes 37 from which it passes to a compressor 21, condensers 24 and tank 12.  The resulting wax slurry containing large wax crystals is drawn off through pipes 41 and is pumped without agitation into a heat-insulated vertical filter L which has been previously cooled to the temperature of the wax slurry by vaporization of propane therein. Wax-free oil passes to receivers 48 and the cakes of wax are removed from the filter by propane vapours or "wash" propane admitted to the filter bags through a pipe 49 connected to a "wash" propane tank 16. The used "wash" propane passes to a tank 51 from which it flows to the chilling chambers A--D.  Wax is removed from the conical base of the filter through a large pipe 55 which may contain a conveyer screw and passes through a drum 57 to a heater 59 maintained under pressure.  Liquid wax containing some propane is withdrawn at the base through a pipe 61 and passes to a flash drum 63 and finally to a stripper 65 in which the wax is treated with live steam.  The wax then passes to a storage tank 69.  Propane liberated in the heater 59 and flash drum 63 passes through pipes 23 and 18 to compressors, condensers &c. for re-use.  The wax-free oil in tanks 48 is drawn through a heat exchanger 15, cooling the wash propane, to a heater 73 maintained under pressure.  The oil is then submitted to further heat treatment in a low pressure flash drum 77 and a steam stripping chamber 79.  Propane vapours liberated in these heaters being liquefied for re-use.  The resulting lubricating oil is led into a storage tank 81.  In the case of viscous oils a small amount of naphtha may be added to the wax bearing oil before the dewaxing treatment.  The process may be carried out with a mixture of liquefied substances, e.g. by using butane as a diluent and propane as refrigerant.  Anti-solvents for wax such as acetone or acid esters may be added alone or mixed with benzene or naphtha.  The filters L, M, N each consist of a chamber 87, Fig. 2, containing a number of filter leaves 90 and having a conical bottom 88 and a concave removable cover 89 which is heat-insulated by cork or asbestos.  Each leaf 90 consists of a coarse screen covered on each side by a finer screen and covered by a canvas element, the members being held together by bolts passing there-through.  The leaves are wedged in a frame with cotton rope to form a liquid tight joint.  In operation, the oil-wax mixture passes through a pipe 44 into the filter previously chilled by vaporization of liquid propane therein. Wax-free oil is discharged from the filter leaves and passes through a flexible pipe to a conduit at the upper side of the filter.  Wax cake is removed from the leaves by admitting gaseous or liquid propane through a pipe 49<a> and the resulting mixture is discharged through a pipe 56.  The filter leaves may be precoated with infusorial earth or fibrous material suspended in light oil or propane and applied by spraying or passing through the filter.